Thanks for your inquiry.
While using the latest version of Aspose.Words i.e. 15.8.0, I managed to reproduce this issue on my side. I have logged this issue in our bug tracking system. The issue ID is WORDSNET-12381. Your thread has also been linked to this issue and you will be notified as soon as it is resolved. Sorry for the inconvenience.
Moreover, in this case, you should just call Document.UpdateTableLayout method before rendering to PDF format; only in rare cases where you confirmed that tables appear incorrect in the output document. I hope, calling this method will help to correct the output. Here is how you may use it:
Document doc = new Document("C:\temp\131404538.docx");